ia64: don't call handle_signal() unless there's actually a signal queued

Sergei and John both reported that ia64 failed to boot in 5.11, and it
was related to signals. Turns out the ia64 signal handling is a bit odd,
it doesn't check the return value of get_signal() for whether there's a
signal to deliver or not. With the introduction of TIF_NOTIFY_SIGNAL,
then task_work could trigger it.

Fix it by only calling handle_signal() if we actually have a real signal
to deliver. This brings it in line with all other archs, too.

Fixes: b269c229 ("ia64: add support for TIF_NOTIFY_SIGNAL")
Reported-by: NSergei Trofimovich <slyich@gmail.com>
Reported-by: NJohn Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Tested-by: NSergei Trofimovich <slyich@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

arch/ia64/kernel/signal.c

@@ -341,7 +341,8 @@ ia64_do_signal (struct sigscratch *scr, long in_syscall)
 	 * need to push through a forced SIGSEGV.
 	 */
 	while (1) {
-		get_signal(&ksig);
+		if (!get_signal(&ksig))
+			break;
 
 		/*
 		 * get_signal() may have run a debugger (via notify_parent())